The invention relates to a device for holding workpieces or pallets for workpieces in a releasable manner on a machining apparatus, comprising a mounting plate which can be connected to the machining apparatus for machining the workpiece, and a clamping pin which can be connected to the pallet or to the workpiece and can be held in the mounting plate in a releasable manner, at least one spring for producing a clamping force for fastening the clamping pin to the mounting plate being provided, and a piston which can be moved hydraulically or pneumatically against the clamping force being provided, and a ball sleeve having balls which can be moved into the ball sleeve by the piston and are arranged so as to interact with the clamping pin in such a way that the clamping pin can be released against the clamping force.
During the machining of workpieces, for example of moulds for die-casting and injection-moulding machines, stringent requirements are imposed on the accuracy of the dimensions. Even after passing through several machining steps, the dimensions of the mould parts may deviate from the specifications essentially by only a few thousands of a millimetre. Modern machine tools permit this precision, inter alia thanks to computer-controlled machining. However, precise machining requires, on the workpiece, precise determination and reproducibility of the zero point of the x-y-z coordinate system for the computer control. The dimensional accuracy of the workpiece depends to a great extent on the accuracy of the clamping devices which are used in order to hold the workpieces in position in a reproducible and releasable manner during the various machining steps.
EP 922529-A1 discloses a unit of the generic type for connecting parts of a palleting system in a releasable manner. The system essentially comprises coupling elements which can be secured to one another in a releasable manner, the first coupling element being arranged in a locating plate for pallets, and it being possible for the second coupling element to be centred and connected in a resilient manner to the first coupling element. A disc-shaped piston, movable by means of hydraulics, springs and a bolt are provided in order to produce the coupling force, the bolt, in one section, forming a ball track together with the second coupling element. For the centring, the first coupling element has at least three spring parts which project along a circular line around the coupling axis and are brought into engagement with the second coupling element.
Starting from this prior art, the object of the invention is to specify a device for holding workpieces in a releasable manner which is composed of few, relatively small individual parts, as small a region as possible being taken up on the workpiece for the releasable fastening.